Variable-Leaf Watermilfoil

Control Options

Cultivation Options

Description of This Plant

Control Options

Mechanical/Physical

Variable-leaf watermilfoil can be removed by raking or seining it from the pond but will reestablish from any remaining fragments and roots.

Fertilization to produce a phytoplankton or algal "bloom" prevents the establishment of most bottom rooted aquatic weeds and produces a strong food chain to the pond fish.

Non-toxic dyes or colorants prevent or reduce aquatic plant growth by limiting sunlight penetration, similar to fertilization. Aquashade is an example of non-toxic dye and other products are available. However, dyes do not enhance the natural food chain and may suppress the natural food chain of the pond.

Biological

Grass carp will seldom control aquatic vegetation the first year they are stocked. They will consume variable-leaf milfoil but it is not preferred. Grass carp stocking rates to control variable-leaf watermilfoil are usually in the range of 7 to 15 per surface acre or more. In Texas, only triploid grass carp are legal and a permit from the Texas Parks and Wildlife Department is required before they can be purchased from a certified dealer.

Chemical

The active ingredients that have been successful in treating variable-leaf watermilfoil include copper complexes (G), 2,4-D (E), diquat (E), endothall (E), triclopyr (E) and fluridone (G). E = excellent, G = good

Navigate and Aqua-Kleenis a granular butoxyethyl ester of 2,4-D and has been effective on variable-leaf watermilfoil. 2,4-D compounds are systemic herbicides. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides.

Reward is a liquid diquat formulation that has been effective on variable-leaf watermilfoil and is very effective if mixed with a copper compound. It is a contact herbicide. Contact herbicides act quickly and kill all plants cells that they contact.

Cutrine Plus, K-Tea, Captain, and Clearigateare all chelated or compound copper herbicides and can be used in a mixture with Reward or Aquathol K. Other chelated or compound copper formulations are available but are not linked to this web site.

Aquathol, Aquathol K, and Aquathol Super K are dipotassium salts of endothall and comes in both liquid and granular formulations. These endothall products have been effective on variable-leaf watermilfoil and can be mixed with copper compounds for additional effectiveness. Contact herbicides act quickly and kill all plants cells that they contact.

Hydrothol 191 is an alkylamine salt of endothall and comes in both liquid and granular formulations. It is a contact herbicide and has been effective on variable-leaf watermilfoil. Contact herbicides act quickly and kill all plants cells that they contact. Hydrothol can be toxic to fish.

Renovate is a liquid triclopyr formulation that is effective on variable leaf watermilfoil. It is a selective broadleaf, systemic herbicide. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides. An aquatically registered surfactant (see the label) will improve the effectiveness of triclopyr.

Sonar and Avast are fluridone compounds, come in both liquid and granular formulations, and have been effective on variable-leaf watermilfoil. These are broad spectrum, systemic herbicides. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides.

One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletions can kill fish in the pond. If the pond is heavily infested with weeds it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion.

One common problem in using aquatic herbicides is determining area and/or volume of the pond or area to be treated. To assist you with these determinations see SRAC #103 Calculating Area and Volume of Ponds and Tanks.

Many aquatically registered herbicides have water use restrictions. For General Water Use Restrictions click here.

To see the labels for these products click on the name. Always read and follow all label directions. Check label for specific water use restrictions.